1. Field of the Invention
The invention relates to inertia reels; and, more particularly, to inertia-actuated reels of the type upon which a belt or strap is stored.
2. Description of the Prior Art
It is well known in the prior art to use inertia reels for restraining and positioning an occupant of a seat on an airplane or in a vehicle or the like. Such reels are adapted to unreel the belt or strap to permit the occupant to lean forward or perform other limited activities. However, during a sudden deceleration of the vehicle or sudden forward movement by the occupant, such reels are adapted to restrain further unreeling therefrom for positive retention of the occupant to prevent injury thereto.
In certain inertia reel devices, spools from part of the device on which surplus belt or strap webbing is stored under spring tension. The restraint system of these devices is normally such that any extending webbing is subject to tension forces at the instant of vehicle impact or the like (which results in a sudden deceleration of the vehicle). In order to restrain the occupant of such vehicles, the unreeling of further webbing is prevented by locking the spool to the frame of the device.
This locking may be achieved by the engagement of a pawl with a ratchet wheel torsionally connected to the spool. The pawl may be urged into engagement by a mechanism which either senses deceleration of the vehicle in the emergency which results, or by the movement of the webbing from the spool as the occupant is thrown forward. In either case, the spool is spinning at the time the pawl is to engage with the ratchet wheel.
In such cases, the first contact between the pawl and the tooth of the ratchet may be tip to tip. At the time this contact occurs, shortly after vehicle impact, the spool is accelerating rapidly, and the kinetic energy of the occupant provides a considerable potential to place heavy loads through the belt and the ratchet wheel on to the pawl. If the radial engagement of the pawl with the ratchet tooth is small, the tooth tip may shear and propel the pawl violently out of engagement. The sudden release of belt tension when this happens, and the continuing forward movement of the occupant relative to the vehicle, causes the spool speed to increase even further, and time intervals between the ratchet teeth passing the pawl tip become too short for subsequent engagements to take place. In such cases, the result is catastrophic in that the restraint system totally fails to function.
In U.S. Pat. Nos. 2,923,492 and 3,386,683, to Walpole et al and Howland, respectively, it is suggested to use a series of latching pawls to engage a toothed wheel attached to and rotating with the spindle of a winding drum. The multiple pawl structure of both patents is substantially the same and, in both cases, the pawls are located so that they engage the teeth of the toothed wheel. Thus, in FIG. 3 of Walpole, et al, for example, the inertia operated pawls 42 are in cocked position (Col. 3, 11 62-65). FIG. 5 shows the inertia pawls 42 in released position. The uppermost pawl 42 has its tip engaging one of the teeth of wheel 40. At the same time, the lowermost pawl 42 is in position to engage a succeeding tooth on wheel 40. However, if the uppermost pawl 42 were to engage the outer tip of its respective wheel tooth, the lowermost pawl 42 might be too close to its respective wheel tooth to engage it in time should the uppermost pawl fail to engage. Thus, the Walpole et al system might fail if the tip of the tooth of the ratchet wheel is broken off when contacted by its respective pawl tip.